1989 Plymouth Sundance fire in throttle body

What caused the fire? If you have spark and fuel, the last thing you need is correct timing. If the timing belt jumped far enough, it could cause a backfire and flames shouting out of the throttle body assembly.

An injector stuck open is extremely rare.

If the timing belt has jumped a few teeth, intake manifold vacuum will be lower than normal. That will be reported by the MAP sensor, and since he has the biggest say in fuel metering calculations, low vacuum equates to acceleration or heavy load, and either condition requires more fuel and is why you may see a lot of fuel spraying from the injector.

Have you checked the timing belt?

Dandy. This is going to be a hugely involved repair that is very technical. For the idle speed problem, ... I hope you're sitting down, ... Drive the car at highway speed with the engine warmed up, then coast for at least seven seconds without touching the pedals.

The high manifold vacuum for an extended period of time is what the Engine Computer needs to see to tell it to relearn "minimum throttle" after the battery was disconnected. Until that is done, the idle speed may be too low for the engine to start unless you hold the accelerator pedal down 1/4", you won't get the nice idle flare-up to 1500 rpm at start-up, and the engine will tend to stall at stop signs.

'95 was the last year for the Shadow / Sundance. They were replaced by the seriously-inferior Neon.

"Highway speeds" simply means not city driving. You're over-thinking this. The Engine Computer just wants to see a steady, non-changing voltage signal from the throttle position sensor, and high intake manifold vacuum so it knows the throttle blade is closed and at its mechanical stop, not being held open by your foot. Those are the conditions the computer looks at to know the throttle is closed and it is supposed to be in control of idle speed. At that instant, it takes the reading from the throttle position sensor and puts it in memory. From then on, any time it sees that voltage, it knows it has to control idle speed.

This relearning of minimum throttle pertains to every Chrysler product with a gas engine since the early 1980s. Most people don't even notice the problem or they're unaware they unwittingly solved the stalling / hard start problem by just driving the car. All they know is the problem went away, if they noticed it at all. I have a hill near my house where I coast down it for about 40 seconds. The off-ramp from the highway nearest me allows me to coast for up to 30 seconds, so seven seconds is really very little time.

Most mechanics will do this procedure after the battery had to be disconnected if the other service requires a test-drive. Other times they should simply inform the customer of the need to do this simple final step. It may be necessary to drive with your right foot on the accelerator pedal and your left one on the brake pedal, which is how a lot of people drive anyway.